1. Field of the Invention
The invention relates to a belt type continuously variable transmission. More particularly, the invention relates to an improvement of a belt type continuously variable transmission provided with a movable sheave sliding mechanism that slides a movable sheave in the axial direction.
2. Description of the Related Art
A belt type continuously variable transmission (hereinafter also referred to as simply “belt type CVT”) is typically provided with two rotating shafts arranged parallel with one another, a primary pulley attached to one of the rotating shafts and a secondary pulley attached to the other of the rotating shafts, and a belt wound around V-shaped grooves in the primary and secondary pulleys. The primary and secondary pulleys each have an upright fixed sheave that is fixed to the rotating shaft (i.e., the primary shaft and the secondary shaft), and an upright movable sheave which slides in the axial direction on the rotating shaft. The V-shaped grooves are formed by slanted portions of the fixed sheaves and corresponding slanted portions of the movable sheaves which face the slanted portions of the fixed sheaves.
In this kind of belt type CVT, the speed ratio can be changed continuously by changing the width of the V-shaped grooves by sliding the movable sheaves in the axial direction of the rotating shafts such that the contact radius of the belt and each of the primary and secondary pulleys changes continuously. That is, since the ratio of the contact radius on the primary pulley side and the contact radius on the secondary pulley side determines the speed ratio of the belt type CVT, this belt type CVT is able to change speed ratios continuously by controlling the width of the grooves of the primary and secondary pulleys.
In a conventional belt type CVT, the movable sheave must be slid in the direction of the rotational axis in order to change speed ratios, so a mechanism (a movable sheave sliding mechanism) is provided in the belt type CVT to slide the movable sheave of the primary pulley. For example, one such movable sheave sliding mechanism slides the movable sheave using driving force from a motor such as an electric motor or a hydraulic motor. JP(A) 6-249310, for example, discloses a belt type continuously variable transmission with just such a movable sheave sliding mechanism.
The movable sheave sliding mechanism in JP(A) 6-249310, however, has the motor positioned at a distance from the movable sheave, and multiple gears for transmitting the driving power from the motor to the movable sheave disposed between the motor and the primary pulley. As a result, room must be made for the movable sheave sliding mechanism which increases the size of the transmission, which is undesirable.